The low grade lymphomas of man (follicular (FL) and small lymphocytic (SLL)) occasionally undergo transformation to more aggressive diffuse large cell lymphomas (DLCL). There exists a clonal relationship between these tumors arising in a single individual as evidenced by constancy of immunoglobulin gene rearrangements and translocation breakpoint (t(11;14) and t(14;18) in SLL and of FL respectively). The molecular basis of this transformation in unknown. These studies propose to isolate and characterize sequences that become activated as a consequence of this transformation event. Isolation of sequences specific to the DLCL will be accomplished by preparing a cell-specific probe by subtraction hybridization thereby eliminating sequences commonly expressed in the follicular and diffuse lymphomas. Unfortunately, the follicular lymphoma tissue cannot be grown in vitro, thus mRNA from the follicular lymphomas is limited. To circumvent this limitation, a novel approach to cloning mRNA as sense-strand single-stranded DNA is proposed that is generally applicable to tissue specimens that cannot be expanded in vitro. cDNA will be directionally cloned into lambda ZAP from which the cloned insert can be expanded as a defective filamentous bacteriophage; the ssDNA genome can then be used in substraction hybridizations in place of RNA as it represents the sense strand. The cell-specific probe will be used to screen cDNA libraries prepared from the DLCL. The clones isolated by this strategy will be characterized as to their expression in follicular and large cell lymphomas as well as normal and stimulated B- lymphocytes. In addition, the transforming potential of these genes will be determined by electroporation of normal B- lymphocytes and FL cells with these gene subcloned into a mammalian expression vector, pRSY-gpt. Further investigations will explore the inability to propagate FL cells in vitro. Utilizing somatic cell hybrids between transformed lymphoma cell lines of EBY-transformed lymphocytes and FL cells, we will determine if the transformed phenotype (assayed as growth in semisolid media) can be transferred to the FL cells.